How do XML elements in activity_quiz.xml become View objects? The answer starts in the QuizActivity class.
When you created the GeoQuiz project, a subclass of Activity named QuizActivity was created for you. The class file for QuizActivity is in the app/java directory of your project. The java directory is where the Java code for your project lives.
In the project tool window, reveal the contents of the app/java directory and then the contents of the com.bignerdranch.android.geoquiz package. Open the QuizActivity.java file and take a look at its contents.
Listing 1.4 Default class file for
package com.bignerdranch.android.geoquiz; import android.support.v7.app.AppCompatActivity; ...